Woven resistance unit



Dec. 17, 1946. SPRAR'AGEN 2,412,843

WOVEN RESISTANCE UNIT Filed Jan. 29, l944 INVENTOR Imam Sprara 0?,

' BY Mmr J ATTORNEYS' Patented Dec. 17, 1946 UNITED STATES PATENT ()FFlCE WOVEN RESISTANCE UNIT Louis Spraragen, Bridgeport, Cnn., assignor to Bridgeport Fabrics, inc, Bridgeport, Conn, a corporation of Connecticut Application January 29, 1944, Serial No. 520,228

18 Claims. 1

This invention relates to electric resistance units, and more particularly to a resistance interwoven with insulating means to form a ribbon or band which may be cut into suitable lengths having a predetermined electric resistance or heating effect and other electrical properties.

Heretofore, in making a resistance unit having a predetermined ohmage or heating effect, two procedures were ordinarily followed. In one, a predetermined length of wire of desired unit resistonce was wound around a coil or spool with the ends of the wire connected to suitable terminal pieces. In the other arrangement, especially for use in electric heating pads, blankets or clothing, resistance wire was led on the surface of the goods and attached thereto by stitching or like means.

According to the present invention, a resistance unit is easily and inexpensively manufactured, preferably in the form of a continuous woven strip, the warp strands of which comprise insulating material, while the weft strands are formed in whole or in part of one continuous resistance wire. In this way, a product is obtained which has substantially the same resistance or heating effect per unit of length throughout the strip. By selecting wire of a particular diameter and material and making the strip uniform in width, the resistance may be predetermined for any given length. Thus, any desired quantity of resistance is obtainable by merely measuring and cutting off the necessary length of strip.

Preferably the warp strands are constituted by fibers in or er that the strip may be wound or rolled on a spool and in order that ut-oif sections of the strip may be bent or shaped to any desired form. Resistance wires of the larger sizes are usually quite still, but since, according to this invention they constitute the weft strands and lie transversely of the strip, when the latter is bent along a transverse line the wires suffer a torsion and twist in response to said bending in a manner to not substantially resist same.

Resistance wires of smaller sizes are substantially flexible and are readily susceptibleto both twisting and bending, and when a strip made up using these smaller sizes, it be easily bent along longitudinal lines as well as transverse. As a result of the zigzag pattern of the resistance wire constituting the web of the strip, the latter possesses non-inductive properties to a marked degree, being considerably superior to coiled resistors in this respect.

The woven resistor of this invention is preferably made with warp threads each comprising a plurality of fibers to form a substantial bundle so that adjacent weft strands comprising the resistance wire are substantially spaced to prevent incidental contact between same, and yet the strip will retain high degree of flexibility. When Nichrome or other wire which oxidizes upon heating is used, there is no necessity for having substantial bulk in the warp strands, since wire of this type is largely self-insulating. Also, when such wire is used, the bare bent portions thereof which lie along the longitudinal edge of the strip generally need not be provided with additional insulation to prevent contact with other objects.

The resistance device of the present invention is not only useful as a resistor or element of an electrical circuit or net work, but is also advantageous when used as a heating element for its heat-producing eifect, such as in a heating pad. In this use of the device, a strip of the resistance unit having a predetermined heating eifect is cut-off from the continuous strip and then placed on a supporting body, such as a blanket for instance, and attached thereto by stitching, and the closely spaced weft resistance wires of the strip provide a uniformly distributed heating effect which is very desirable in such devices.

When the resistor strip of the present invention is used for any purpose where it becomes heated, whether it be in a heating pad or other device, I have found it to be particularly advantageous to employ flexible plastic fibers to make up the warp strands of the stri' one type of such fiber employed with success being spun glass. This fiber is especially heat-resistant and noninflammable, has hi h tensile strength, heat conductivity and radiation factors, and in the fine sizes is extremely flexible, and these properties impart qualities to the strip which result in numerous advantages as will be later brought out.

Anot advantage of the present invention is that it may be used as a heating covering or casing, as, for example, for heating the pipe lines in an airplane which, at high altitudes, are susceptible of freezing. For this use, in the form at present preferred, the resistance device, as described above, is woven double to form a flattened sleeve or tube which, after being cut to lengths, may be spread open and the pipe, etc. fed into it. Or, the flat woven strip may be wrapped around the pipe line in helical fashion, or longitudinally folded thereabout.

In the use of the device of this invention after a section of the strip has been cut-off for use, the resistance wire may be connected to currentconducting means in any suitable manner. For

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instance, the ends of the strip may be unravelled to produce a free strand of the wire which may be fastened to a binding post, etc. Or, if desired, the ends of the strip may receive an eyelet or clamp which would contact with the resistance wire at or near the end of the strip. If it should be desired to tap into the resistance unit between the ends thereof, this may also be done by piercing the strip with an eyelet, staple, etc., or by clamping a conductor upon the strip and in contact with the resistance wire.

Other features and advantages will hereinafter appear.

In the drawing Figure 1 is a perspective View of a tape made according to this invention.

Fig. 2 is a fractional sectional view of the same taken along line 2-2 of Fig. l on an enlarged scale.

Fig. 3 is a plan view showing a tape, made according to the invention, fastened to a piece of fabric.

a Fig. 4 is a side elevational view showing the tape of Fig. 1 helically wound around a pipe line,

Fig. 5 is a plan view showing the tape of Fig. l encircling a portion of a pipe line.

Fig. 6 is an end view of a modified form of the invention showing a double woven strip constituting a flattened tube.

Fig. '7 is a side elevation of the tube of Fig. 6, receiving a pipe line.

Fig. 8 is an end view showing the double strip of Fig. 6 with an interposed insulating strip.

The resistance device of the present invention, in the form illustrated in Figs. 1 and 2, comprises a strip ill which is substantially fiat and in the form of a continuous tape. This tape is made by interweaving strands of insulating material with a single continuous strand of wire in such a manner that the tape functions as an elongate resistor having a value which varies according to its length. This is accomplished by a weaving process wherein, as seen in Fig. 2, strands i l of insulating material are arranged to form the warp of the tape, and a single electrical resistance wire [2 is woven back and forth between the warp strands to form weft of the tape, all in a manner that, as the weaving of the tape proceeds, the wire I2 is interwoven to follow a closely spaced zigzag folded path. According to this arrangement, the weft of the tape I0 provides a definite electrical resistance, which may be utilized in a circuit or other device by making connections to the ends l3 and M of the wire H.

The spacing between each adjacent pair of weft wires of the tape is substantially a constant, so that for a given weave there are a predetermined number of weft wire folds per inch of length. Also, the width of the tape is closely controlled, and as a result each inch of length of the tape lil contains a fixed predetermined length of continuous weft wire, and therefore represents a fixed Value of electrical resistance. This makes it possible to utilize the tape H] as an elongate resistor which has a resistance value directly proportional to its length, and as such the tape may be transversely cut ofi so that a given value of resistance is obtained by a given measured length of tape. Or, the heating effect of the wire may be considered, so that for a given voltage a certain length of the tape will produce a certain amount of heat.

The strands H which comprise the warp of the tape ii! are preferably of insulating material which is flexible so that the tape may be readily bent or shaped. When larger sizes of resistance wire, which are usually quite stiff, are employed in the tape, they tend to stiffen it. But, since they are the weft strands and therefore lie transversely of the tape, there is no substantial resistance to transverse bending or shap- Where the smaller sizes of resistance wire, which are substantially flexible, comprise the weft strands [2 of the tape, it may be easily bent or shaped longitudinally as well as transversely.

As illustrated in Fig. 2, each warp strand ii may comprise a plurality of fibers of insulating material and the substantial bundle formed thereby spaces and prevents contact between adiacent weft strands 12 of continuous resistance wire and also functions to embed the resistance wire in the tape to prevent incidental contact between the Wire and other objects. When nichrome, or other wire which oxidizes upon heating and becomes self-insulating, is used, there is no necessity for having the Warp strands of insulating material in such bulk. When that type of wire is used, the side edges iii of the tape need not be insulated against contact with other objects. I

The resistance device of the present invention may be advantageously used as a heating ele ment, and as such constitutes a, new article of manufacture. In this use of the device, in the form illustrated herein as exemplary thereof, see Fig. 3, a strip lea having a. desired predetermined heating effect, as heretofore described, is attached to supporting body it, as, for example, a blanket, heating pad or heat transmitting material by a suitable attaching means, as by stitching, which passes thru the strip iila and the supporting body. It will be seen that this use of the resistance device provides for great saving of time over the practice heretofore in use, where individual wires were sewed on the surface of a supporting body.

In the illustration, Fig. 3, the strip ifla is provided with eyelets 18 or the like, which contact the ends of the resistance wire at or near the ends of the strip Eta, but the latter may be connected to current-conducting means in any suitable manner. When the wire of the strip is connected to a current supply, a uniform and distributed heating occurs which is evenly transmitted to the supporting body it, providing an efficient heating device.

In connection with this use, I have found it to be advantageous to make the warp strands in the strip lila of flexible plastic fibers, preferably spun glass. In the smaller diameters these fibers are exceedingly flexible and possess high tensile and impact strength, and when woven with wire into a cloth strip the texture is smooth and pliable. When such a strip is used in a heating pad, for. example, the pad does not have a lumpy feel, but-is uniform in thickness, and easily formed into various shapes. Due to the resistance of the glass fibers to damage-from impact, a heating pad made with such a strip will be mor rugged and less likely to fail when used roughly. Moreover, glass fibers are better heat conductors than woolen, cotton, silk'and other fibers, and better radiators. They are also noninflammable, and the resistor strip ltd, when made up using glass fibers in th warp strands, provides a distinct improvement overany prior article designed for similar use, since'the heating is safer, more direct and more quickly transferred, and also more uniform.

Should the strip Illa, when made with warp strands composed of glass fibers, be used as a resistor where theheating is incidental to its main use, it still possessesmarked advantages, since it provides a flexible unit which may be made to conform to difiercnt shapes, is rugged and noninflammable, and has high heat conduction and radiation characteristics which are desirable in this type device.

The resistor of the present invention lends itself to use as a heating casing or covering, as, for example, for heating pipe lines in an airplane which are susceptible to freezing. For this use of the invention. as illustrated in Fig. i, the resistance tape [0b, which has interwoven therein warp strands of flexible glass fibers is wound helically around a pipe IS, the ends being fastened in some suitable manner. If the pipe is metallic, it may be desirable to first wrap it with an insulating coating (see Fig. 5) so that the wires of the tape are prevented from accidentally touching the metal andbecoming short-circuited. Or the tape itself may be wrapped with an insulating coating to effectively prevent adjacent edges from short-circuiting. As shown in Fig. 5, a fiat resistor tape lfic may be curled about its longitudinal axis around a pipe line H30 in the form of a sleeve which substantially retains its given shape. The sleeve may be positively maintained in position about the pipe by securing together the adjacent longitudinal edges 20 of the tape, as by laces 2 i. As shown, a cord l3 may be interwound with the tape lfib.

A modified form of the invention, as shown in Fig. 6, is also applicable to heating pipe lines and strands, and resistance wire weft, the layers be- 1 ing connected along both edges by the weft.

Referring to Fig. 7, the fiat sides of the tube 22' at one end 23 may be spread apart and a pipe line 24 or like object fed into the tube whereby the latter effectively and completely encases the line. When in this position, the tube 22 forms a sheathing, the weft of which is a continuous helical resistance wire. Connection may be made to the resistance wire by clamps encircling the tube, or by eyelets or other means, so that a heating may be passed therethrough for warming the pipe.

It will be understood that the above uses are merely shown as examples and not by way of limitation, and that the device may be used in many other ways by skilled technicians in the various arts.

I claim:

1. As a new article of manufacture, a resistor comprising a fabric having warp of strands of extruded insulating fibers and weft comprising solely a single continuous piece of uncovered resistance wire interwoven with the warp to form a pattern wherein no portion of the wire contacts 1 tween any two weft strands taken at points along a side edge of the fabric is directly proportional to the distance between said points.

4. The invention as defined in claim 1, in which the warp strands consist of bundles of glass fibers, and in which the resistance wire is suitable for heating use whereby the resistor is adapted to function as a flexible heating element.

5. The invention as defined in claim 1, in which the warp strands are flexible and non-inflammable, and in which the resistance wire is suitable for heating use whereby the resistor is adapted to function as a flexible heating element.

6. The invention as defined in claim 1, in which the warp strands consist of bundles of glass fibers whereby the resistor is rendered substantially non-inflammable.

'7. The invention as defined in claim 1, in which the warp strands consist of bundles of plastic fibers whereby the resistor is adapted to dissipate heat by both conduction and radiation.

8. The invention as defined in claim 1, in which the warp strands are flexible and non-inflammable, in which the resistance wire is suitable for heating use, and in which the strands of weft constituted by said wire which are adiacent each other are separated by substantially the thickness of a warp strand whereby the spacing between said weft strands is a minimum so that the resistor will function as a flexible heating element providing substantially uniformly distributed heating over its entire surface when energized.

9. The invention as defined in claim 1, in which the warp strands are flexible, heat conducting and radiating, and in which the resistance wire is suitable for heating use whereby the resistor is adapted to function as a flexible heat-dissipating heating element.

10. The invention as defined in claim 1, in which the warp strands are more flexible than the weft wire, having a bulk relative to the wire size whereby the weaving of the strip substantially embeds the wire therein below the surface defined by the warp to minimize incidental contact of said wire with other objects.

11. The invention as defined in claim 1, in which the warp fibers are more flexible, and of smaller diameter than the weft wire whereby the weaving of the strip substantially embeds the wire therein below the surface defined by the warp to minimize incidental contact of said wire with other objects.

12. A resistor comprising a pair of fiat equal width, woven strips superposed one on the other, each having warp strands of plastic insulating fibers and the weft of both strips comprising a single continuous piece of bare resistance wire interwoven alternately with the warp strands of each strip to form a pattern wherein no portion of the wire contacts any other portion thereof, so that a current will flow through same which follows solely a series path.

13. A resistor comprising a woven tube having warp of strands of insulating fibers and weft comprising solely a single continuous piece of resistance wire interwoven with the warp to form a helical pattern wherein no portion of the wire contacts any other portion thereof so that a cur rent will flow through same which follows solely a series path.

14. The invention as defined in claim 12, in which there is a flat strip of insulating material interposed between the woven strips to separate same for preventing incidentallcontact between their respective wefts. 7

15. A heating pad having a heating element comprising a fabric having warp of strands of plastic insulating fibers and weft comprising solely a single continuous piece of bare resistance wire interwoven with the warp to form a pattern wherein no portion of the wire contacts any other portion thereof, and a fabric body superposed on the heating element and stitched thereto to isolate same from a user. a

16. A heating element comprising a woven strip having warp strands each consisting of a bundle of glass fibers, and having a single continuous bare resistance wire alone constituting the weft of the strip, the bulk of the Warp strands being such that strands of weft which are adjacent each other are spaced and prevented from contact, and the size of the wire having a relation to the bulk of the warp strands such that the weaving of the strip embeds the wire therein below the surface defined by the warp, said spacing between the adjacent weft strands being sub stantially equal to a constant, and the width of the strip being uniform whereby. the electrical resistance between any two weft strands taken at points equidistant from a side edge of the strip is directly proportional to the distance between said points. b Y

17. A resistor comprising a fiat woven strip having warp of strands of extruded insulating fibers and weft consisting of a single continuous piece of bare resistance wire alone interwoven with the warpto form a zigzag pattern wherein no portion of the wire contacts any other-portion thereof, and wherein the inductive efiect of each weft strand is reduced by the next weft strand to produce a strip of substantially noninductive characteristics. a i

18. The invention as defined in claim 1, in which the warp strands are flexible, and in which the resistance wire is of small size to be easily bent whereby the resistor may be readily shaped to fit various forms.

LOUIS SPRARAGEN. 

